1. Field of the Invention
The present invention relates to an engine control apparatus that is provided with a valve operating mechanism using a timing wrapping member such as a timing belt, etc., and in particular, it relates to such an engine control apparatus that can determine the state of an engine based on a phase shift or deviation of a camshaft relative to a crankshaft generated due to a secular change (expansion, wear, etc.) in a timing wrapping member by detecting such a phase shift upon occurrence thereof, inform, if determined that the timing wrapping member is abnormal, a driver or operator of the state of occurrence of abnormality in the timing wrapping member by performing appropriate processing such as warning, stopping fuel supply, etc., based on the output of an abnormality determination signal, and stop the operation of an engine whose timing wrapping member is in an abnormal state.
2. Description of the Related Art
In general, a valve operating mechanism for an engine includes a timing wrapping member such as a timing belt, etc., to drive an intake cam and an exhaust cam in synchronization with a crankshaft. In addition, there are also provided a crank angle sensor for detecting the rotational position of a crankshaft and a cam angle sensor for detecting the rotational position of a camshaft. A cam phase (the rotational phase of the camshaft relative to the crankshaft) is obtained based on the detection signals of the crank angle sensor and the cam angle sensor.
The crank angle sensor outputs a crank angle signal in the form of a pulse at each unit crank angle, as is well known, but it is constructed such that there is a pulse loss generated in a part of the crank angle signal, and the position of a lost or missing pulse is detected from a change in the output interval of crank angle signal pulses. Then, the cam phase is calculated from a cam angle signal pulse following a crank angle reference position signal pulse which is output as a reference position of the crank angle signal and which is detected at the first timing after the lost pulse position.
However, the phase of the camshaft with respect to the crankshaft might shift or deviate in a retard angle direction from its initial phase at the time of installation of the engine due to a secular or time-related change (expansion, wear, etc.) of the timing wrapping member. If the phase of the camshaft shifts in this manner, the opening and closing timing of intake and/or exhaust valves changes toward the retard angle direction, too, so the air fuel ratio of a mixture in each engine cylinder is adversely affected, thus posing a various kinds of problems such as generation of knocking, reduction in fuel mileage, the deterioration of exhaust emission, etc.
In conventional engine control apparatuses, it has been proposed that in order to avoid the occurrence of the problems as stated above, the state of an engine is determined by the use of the phase of a camshaft relative to a crankshaft, and upon determination of the presence of an abnormality, appropriate measures such as warning, stopping fuel supply, etc., should be taken based on an abnormality determination signal generated (see, for example, a first patent document (Japanese patent application laid-open No. 2001-164980) or a second patent document (Japanese patent application laid-open No. 2002-309994)). In the above-mentioned first patent document, when the detected phase of the camshaft exceeds an upper limit abnormality determination threshold or falls below a lower limit abnormality determination threshold, an abnormality determination signal is output so as to perform the operation of a warning device or an engine stopping device. Also, in the above-mentioned second patent document, when a selected phase of the camshaft exceeds an upper limit abnormality determination threshold, an abnormality determination signal is output so as to operate a warning device and/or an engine stopping device. In both of the above-mentioned first and second patent documents, each of the abnormality determination thresholds is defined as a reference phase (an upper limit threshold value or a lower limit threshold value) for a central value of an initial phase at the time of engine designing, which can not generate the above-mentioned problems.
In general, if there does not exist at all any factor to induce variation in control response at the time of engine installation, such as manufacturing errors of a crank angle sensor and a cam angle sensor (parts variation, mounting errors such as mounting variation, etc.), parts accuracy errors of sensor plates (form or shape tolerances, etc.), an amount of shift or deviation of the phase of the camshaft and that of the initial phase thereof in any engine coincide with the amounts of shifts or deviations of corresponding central values, respectively, at the time of engine designing, so it is possible to achieve accurate abnormality determination processing by the use of the above-mentioned abnormality determination thresholds.
However, it is not avoidable that the above-mentioned manufacturing errors exist in the actual assembly or installation of the engine, and hence the initial phase of the camshaft does not necessarily completely coincide with the initial phase of the central value thereof at the time of engine designing. As a result, in the abnormality determination processing using the above-mentioned abnormality determination thresholds, there can be a false or incorrect detection (i.e., determined as abnormal in spite of being normal) or an impossibility of detection (i.e., not determined as abnormal in spite of being abnormal) in the vicinity of the lower or upper limit abnormality determination threshold, thus making it impossible to achieve abnormality determination processing with a high degree of precision.
On the other hand, when abnormality determination processing is intended to be made with a new abnormality determination threshold being set while admitting the existence of manufacturing errors, the abnormality determination thresholds in this case should be set in the following manner. That is, the lower limit phase for a minimum initial phase in the allowed manufacturing error or tolerance is set as a lower limit abnormality determination threshold, whereas the upper limit phase for a maximum initial phase is set as an upper limit abnormality determination threshold, thus resulting in a wider range for the lower limit and the upper limit.
Accordingly, even if the abnormality determination thresholds newly set in this manner are used, there will be an impossibility of detection (not determined as abnormal though it is abnormal) in the vicinity of the abnormality determination thresholds, so it is still impossible to achieve abnormality determination processing with a high degree of precision.
Here, specific reference will be made to problems in the conventional abnormality determination processing using a first threshold setting and a second threshold setting for abnormality determination according to the above-mentioned first and second prior art patent documents while referring to FIG. 12.
FIG. 12 is a timing chart showing an abnormality determination operation at the time of a phase shift due to a secular change of the above-mentioned timing wrapping member, wherein the air fuel ratio of a mixture is deteriorated by a change in the valve opening and closing timing due to the secular change, thus representing a state in which knocking, reduction in fuel mileage, deterioration in exhaust emission or the like can be generated. In FIG. 12, the axis of abscissa corresponds to the phase (crank angle position) from a crank angle reference position. In FIG. 12, a crank angle reference position signal and a cam angle signal calculated with respect to the crank angle reference position signal are shown in association with the first and second threshold settings. In addition, the respective initial phases of engines A, B installed with their initial phases lying within a manufacturing tolerance range are also shown in association with each other.
Now, in an engine in which the initial phase of a central value at the time of engine designing is M0, when the value of the detected phase falls below a reference phase MMN of an angle more advanced than that of the initial phase M0, or when the detected phase value exceeds a reference phase MMX of an angle more retarded than that of the initial phase M0, the air fuel ratio of a mixture is deteriorated to cause the above-mentioned problems, so it should be determined that “the engine is in an abnormal state”. On the other hand, since the above-mentioned problems are not caused when the detached phase is within a range from the advanced side reference phase MMN to the retarded side reference phase MMX, it should be determined that “the engine is not in an abnormal state”. That is, in the engine of the initial phase (central value) M0, the advanced side reference phase MMN is set as a lower limit threshold for the first threshold setting, and the retarded side reference phase MMX is set as an upper limit threshold for the first threshold setting. At this time, the phase of the lower limit (MMN) and the phase of the upper limit (MMX) are set as the first threshold setting.
Hereinafter, an explanation will be given while taking account of the engines A, E assembled or installed normally in a factory with their initial values being set within the allowed manufacturing error or tolerance with respect to the initial phase M0 of the central value at the time of engine designing.
First of all, in case of the engine A, let us assume that the phase in which the above-mentioned problems (the deterioration of the air fuel ratio) with respect to an initial phase A0 will not be caused upon detection of the initial phase A0 is in a range between a lower limit phase AMN and an upper limit phase AMX. At this time with the engine A, they are shifted or deviated from the initial phase A0 due to a secular or time-related change of the timing wrapping member. Here, when looking at the state of the engine A, the former or earlier two phases A1, A2 exist between the lower limit phase AMN and the upper limit phase AMX and hence there is no possibility of causing the above-mentioned problems (the deterioration of the air fuel ratio), so it should be determined that “the engine A is not in an abnormal state (i.e., in a normal state)”. On the other hand, the latter or later two phases A3, A4 exceed the upper limit phase AMX and can cause the above-mentioned problems (the deterioration of the air fuel ratio), so it should be determined that “the engine A is in an abnormal state”.
Also, in case of the engine B, let us assume that the phase in which the above-mentioned problem (the deterioration of the air fuel ratio) with respect to an initial phase B0 will not be caused upon detection of the initial phase B0 is in a range between a lower limit phase BMN and an upper limit phase BMX. At this time, if phases B1, B2 and B3 have been detected over time with the engine B, they are shifted or deviated from the initial phase B0 due to a secular or time-related change of the timing wrapping member. Here, when looking at the state of the engine B, the former or earlier two phases B1, B2 exist between the lower limit phase BMN and the upper limit phase BMX and hence there is no possibility of causing the above-mentioned problems, so it should be determined that “the engine B is not in an abnormal state (i.e., in a normal state)”. On the other hand, the latter or later phase B3 exceeds the upper limit phase BMX and can cause the above-mentioned problems, so it should be determined that “the engine B is in an abnormal state”.
As described above, let us assume that the abnormality determination processing according to the above-mentioned first and second prior art documents (i.e., the abnormality determination processing on the initial phase M0 based on the first threshold setting) is performed with respect to the engines A, B which are installed with their initial phases lying within the manufacturing tolerance range for the initial phase M0 of the central value at the time of engine designing. At this time, the former or earlier phase A1 of the engine A is below the lower limit phase MMN, so it is determined that the engine is “in an abnormal state”, instead of being in a “normal state” that should be determined originally or intrinsically. On the contrary, the latter or later phase A3 of the engine A does not exceed the upper limit phase MMX, so it is determined that the engine is “not in an abnormal state (in a normal state)”, instead of being in an “abnormal state” that should be determined originally. In the other phases A2 and A4, there is no difference between them and the states that should be determined originally, thus posing no particular problem. On the other hand, the phase B2 of the engine B exceeds the upper limit phase MMX, so it is determined that the engine is “in an abnormal state”, instead of being in a “normal state” that should be determined originally. Here, note that in the other phases B1 and B3, there is no difference between them and the states that should be determined originally, thus posing no particular problem.
Thus, since there exists the manufacturing tolerance range for the initial phase M0 of the central value at the time of engine designing, when abnormality determination processing is executed based on the first threshold setting for the initial phase M0, there can be a case where a determination different from the state that should be determined originally (i.e., determined as an abnormal state though it should be determined as not an abnormal state, or determined as not an abnormal state though it should be determined as an abnormal state), is made.
Now, reference will be made to a case in which abnormality determination processing is further executed separately by using a new second threshold setting in FIG. 12. In this case, the determination threshold is set in consideration of an initial phase within the range of a manufacturing error or tolerance permitted for the initial phase of the central value at the time of engine designing, as stated above. That is, the lower limit threshold is set to a phase value with which the above-mentioned problem can not be caused in an engine with a minimum initial phase lying in the manufacturing tolerance range among engines which are installed normally at a factory with their initial phases within the manufacturing tolerance range for the initial phase M0 of the central value at the time of engine designing. Also, the upper limit threshold is set to a phase value with which the above-mentioned problem can not be caused in an engine with a maximum initial phase lying in the manufacturing tolerance range among engines which are installed normally at a factory with their initial phases within the manufacturing tolerance range for the initial phase M0 of the central value at the time of engine designing.
In the engines A, B installed with their initial phases lying in the manufacturing tolerance range for the initial phase M0, a minimum phase among the lower limit phase MMN and the upper limit phase MMX of the respective engines A, B, i.e., the lower limit phase AMN for the initial phase A0, is set as a lower limit threshold according to the second threshold setting for the initial phase M0, whereas a maximum phase among the lower limit phase MMN and the upper limit phase MMX, i.e., the upper limit phase BMX for the initial phase B0, is set as an upper limit threshold according to the second threshold setting for the initial phase M0. When abnormality determination processing is carried out based on the second threshold setting thus set, the phase A3 in the engine A does not exceed the upper limit phase MMX, and hence instead of being determined as an “abnormal state” that should be determined originally, it is determined that the engine is “not in an abnormal state (in a normal state)”. Here, note that in the other phases A1, A2 and A4, there is no difference between them and the states that should be determined originally, thus posing no particular problem. On the other hand, in case of the engine B, in the phases B1, B2 and B3, there is also no difference between them and the states that should be determined originally, thus posing no particular problem. Thus, even if the abnormality determination processing is executed based on the second threshold setting newly set, the manufacturing tolerance range is included in the second threshold setting. As a result, the threshold setting range (from the lower limit to the upper limit) is widened or increased, so there might be a case that the engine is determined to be not in an abnormal state, though it should be originally determined that the engine is in an abnormal state.
FIG. 13 is an explanatory view that illustrates the above abnormality determination results in a table, wherein the respective determination processing results based on the first and second threshold settings are shown together with the engine states (original or intrinsic states) that should be originally determined. In FIG. 13, when a determination result and a corresponding original state coincide with each other, it is represented, as the absence of difference, by “O”, whereas when they do not coincide with each other, it is represented, as the presence of difference, by “X”.
As will be clear from FIG. 13, when abnormality determination processing is executed on the detected phase of an engine, which is installed normally at a factory with its initial phase lying within the manufacturing tolerance range, for the initial phase of the central value at the time of engine designing by using the abnormality determination thresholds (regardless of the first or second threshold setting) as they are, there is a possibility that an abnormality determination result is output which is different from the state that should be determined originally in each individual engine, and it is impossible to achieve abnormality determination processing with a high degree of precision.
In the conventional engine control apparatuses, the abnormality determination thresholds are used for abnormality determination as they are with respect to a detected phase of an engine which has been installed normally at a factory with its initial phase lying within a manufacturing tolerance range for the central value of an initial phase at the time of engine designing. As a result, there arises the following problem. That is, when an abnormal state of the engine is determined with respect to a phase shift or deviation due to a secular change of the timing wrapping member, by using an abnormality determination threshold setting intended for only a phase shift or deviation set at the time of engine designing, there will be a possibility that a result (incorrect determination or impossible detection) different from the state that should be determined originally in each individual engine at the time of abnormality determination might be output due to the existence of manufacturing errors, thus making it impossible to achieve highly accurate abnormality determination processing.